Boiler construction



June 18, 1957 J. w. THROCKMORTON ETAL BOILER CONSTRUCTION 5 Sheets-Sheet 1 Filed March 29, 1954 IN V EN TORS. JOHN W. THROC KMORTON 'JOHN S. WALLIS BY 4. 9. MM

ATTORNEY.

June 18, 1957 J. w. THROCKMORTON ET AL 2,796,052

BOILER CONSTRUCTION 5 Sheets-Sheet 2 Filed March 29, 1954 FIG. 5

FIG. 6

IN V EN TORS. JOHN W. THROCKMORTON JOHN s. WALLIS BY ATTORNEY.

June 18, 1957 J. w. THROCKMORTON ET AL 2,

BOILER CONSTRUCTION Filed March 29, 1954 3 Sheets-Sheet 5 l .JE I u INVENTORS. JOHN W. THROCKMORTON JOHN S. WALLIS BY K- ATTORNEY.

States BOILER CONSTRUCTION Application March 29, 1954, Serial No. 419,342

9 Claims. (Cl. 122-356) This is a continuation-in-part of application Serial No. 173,301 filed July 12, 1950 for Boiler Construction, now abandoned.

This invention relates to improvements in boiler construction, and refers more particularly to a cylindrical or multi-sided upright furnace in which the sourceof combustion gases is located in the bottom, and the combustion gases are discharged through an integral stack or a flue gas outlet at the top.

The construction provides some features which are improvemen-ts upon Wallis et al. Patent No. 2,340,289, issued February 1, 1944 and others which are improvements upon Throckmorton et :al. Patent No. 2,375,505, issued May 8, 1945. Also some features are provided which are improvements upon Throckmorton et a1. Patent No. 2,621,636, issued December 16, 1952.

In the construction of the illustrated embodiments of the invention, a single vertical drum is within and coaxial with the furnace casing, which has a greater diameter in its lower radiant zone than in its upper convection zone,

thus providing a restricted annular passage for combustion gases in the latter zone. This is to maintain the proper velocity of the combustion gases through the convection zone without resorting to an inverted conical bafile or the like, such as is disclosed in Throckmorton Patent No. 2,375,505, for example.

One or more circular banks of heating tubes which are concentric with the drum are joined to the bottom of the drum and to the drum above the lower portion of the convection zone. One of these banks may be adjacent to the surface of the drum so as to shield the latter from receiving any appreciable amount of direct radiation.

The unit may be equipped with a forced draft fan, and/or an economizer, and/ or a superheater, for greater efiiciency.

Substantially the entire weight of the drum and the other heating elements is supported by the foundation of the furnace casing which thus can be relatively very light. In Throckmorton et a1. Patent No. 2,375,505, the entire heating surface assembly is hung from the top of the structural steel; therefore, the entire casing must be made sufiiciently strong to support the entire weight of the drum, liquid and tubes.

A vertical cylindrical bafile within the drum and coaxial therewith prevents direct radiation from impinging upon the main body of liquid within the drum, and since the space within the baffie functions as a downpipe, circulation of the charging stock is unimpaired by vaporization in the downpipe. In Throckmorton et a1. Patent No. 2,375,505, the downpipe is exposed to direct radiation from the burners, and any vapor generation in the downpipe decreases the density of the downflowing liquid, which in turn reduces the circulation. tions of the invention there are tubes which protect the drum, and if the drum absorbs heat, the baffle prevents any vapor from contaminating the downflowing liquid.

Accordingly, it is an object of the invention to provide a boiler construction with a single drum which combines atent C In most modifica- 2,796,052 Patented J1me 18, 1957.

a heat aborbing space, a vapor-separating space, and a downpipe totally surrounded by fluid. v

It is another object to provide a single drum boiler of vertical construction wherein the drum rests on the boiler foundation and carries the entire load of the heating surface assembly, thus reducing construction costs by making possible relatively light construction of the boiler casing.

It is a further object to provide a single drum boiler of vertical construction wherein the need for a conical bafile and sleeve is obviated.

It is still another object to provide a boiler construction in which the downpipe is not exposed to direct radiation from the burners, thus maintaining all fluid in the downpipe in-the liquid phase, thus providing unimpaired circulation.

Yet another object is to provide a boiler comprising a vertical furnace that has a central cylindrical drum extending the length of the furnace, and a shell concentric with the drum with provision for a relatively wide and relatively tall annular furnace chamber at the lower portion while a relatively shorter narrow annular chamber is formed at the upper portion of the furnace. There being included fuel burners at the bottom of the Wide annular chamber which are directed axially upward within the annulus to heat the boiler primarily by radiant heat Without impinging directly against either side of the chamber. There being at least one bank of vertical tubes close to one wall of the wide annular chamber and extending through the narrow annular chamber with extended surfaces on the tubes in the narrow chamber to receive heat primarily by convection in this narrow chamber, the tubes of this bank being connected to the central drum near the extremities thereof.

Other objects and advantages will appear from the following description taken together with the accompanying drawings in which:

Fig. 1 is a sectional elevation of a furnace embodying the invention;

Fig. 2 is a sectional view taken along line 2-2 of Fig. 1;

F Fig. 3 is a sectional view taken along line 3-3 of Fig. 4 is a sectional elevation of a first modification of the furnace of Figs. 1, 2 and 3;

Fig. 5 is a sectional view taken along line 55 of Fig. 4;

Fig. 6 is a sectional view taken along line 6-6 of Fig.

Fig. 7 is a sectional elevation of a second modification of the furnace of Figs. 1, 2 and 3;

Fig. 8 is a sectional view taken along line 8-8 of Fig. 7; and

Fig. 9 is a sectional view taken along line 9-9 of Fig. 7.

Referring first to Figs. 1, 2 and 3 of the drawings, the illustrated unit includes a vertical, cylindrical casing indicated generally at 14, which has a larger diameter in its lower or radiant portion 16 than in its upper or convection portion 18. The casing 14 is lined with refractory material, is supported upon a foundation 19, and carries an integral stack 17. I

A single vertical, cylindrical drum 20 is coaxial with and within the casing 14 and extends substantially from the bottom to the top thereof. The drum 20 is mounted upon a skirt 22 which rests upon the foundation 19. Thus the entire weight of the drum 20 is supported by the foundation 19. I

The lower portion 16 of the casing and the surface of the drum 20 define a radiant zone 21, which, when the boiler is in operation, will be subjected to direct radiation, and the upper portion 18 of the casing and the surface of "ice arcaosa the drum define a convection zone 23, which, when the boiler is in operation, will be subjected principally to convection heating. It is particularly significant that the annular convection zone 23 forms a restricted passage for the combustion gases, which, as they travel upward, away from the burners (to be described), and into the convection zone 23, tend to lose velocity; by thus restricting the cross-sectional area of their path, proper velocity is maintained, without necessity for an inverted conical baflle and sleeve, such as is shown in Throckmorton et al. Patent No. 2,375,505.

Two concentric banks of vertical heating tubes 24 and 26 are adjacent to the surface of the drum and to the casing 14, respectively.

The tubes 24 and 26, which are fitted with extended surfaces or fins in the upper or convection zone and are bare in the lower or radiant zone, are connected to the drum 20 near its bottom and near its top, and are entirely supported by the drum 20. Certain of the tubes 26 are bent at the bottom to provide space for burners a 28, which are installed through the floor of the unit, between the inner and outer banks of tubes 24 and 26, respectively.

The drum 20 is equipped with a vertical cylindrical baffle 48, which is adjacent to the inner surface of the drum 20 and is coaxial therewith. The baflie 48 ex tends from a point near where the lower ends of the tubes 24 and 26 are joined to the drum 20 to a point above the lower portion of the convection zone 23, forming an annular passage 43 between the baffle 48 and the drum 20. Thus if any liquid between the drum 20 and the bafile 48 should be vaporized, it will rise through the annular passage 43 and not disturb the downward flow of liquid in the center of the drum 20, which center functions as a downpipe.

Any vaporization of liquid in the downpipe decreases the density of the downflowing liquid, which in turn impairs the circulation.

The downpipe not being exposed to direct radiation, the downflowing liquid is not contaminated by vapor, so that the feed to the bottoms of the tubes 24 and 26 is complet'ely in the liquid phase.

The tubes 24 provide further protection for the drum 20 against receiving direct radiation.

The baffle 48 is of very light construction and may be supported by any suitable means, such as spot welding at 49 to the inner surface of the drum 20.

To attain very high efliciency, the unit illustrated in Figs. 1, 2 and 3 is equipped with a forced draft fan 30, an economizer or preheater 32, and superheater tubes 34. As will appear more clearly below, these elements may be omitted.

The economizer 32 comprises a bundle of interconnected heating tubes 33 in the stack 17 above the drum 20 and is wholly supported thereby. The economizer 32 is fed through an inlet 36, and its outlet 38 provides means for filling the drum 20 with liquid 40 to a predetermined level 42, leaving a vapor zone 44 in the top section of the drum 20.

The superheater tubes 34, which also are supported by the drum 20, have their top ends connected to the drum 20 near the top of the vapor zone 44, and extend vertically adjacent to the surface of the drum 20, replac- 'mg some of the tubes 24 (see Fig. 3). The bottom ends of the superheater tubes 34 do not connect with the bottom of the drum, but are looped back upward and terminate in a superheater outlet 46.

The superheater may be made in any proportion to the rest of the furnace, depending upon the degree of superheat desired.

Not all of the charging stock will be vaporized in passing through the tubes 24 and 26. But it is desirable smaller cylindrical baflle 51 may be provided within the drum 20 and near its top, in the region where the upper ends of the tubes 24 and 26 are joined to the drum 20, in accord with the British patent of Throckmorton No. 664,019 issued April 23, 1952. The baffle 51 is sup ported from the drum 20 by means of a solid ring 53 around the top of the bafile 51. Thus an annular chamber 55 is formed which is closed at its top and open at its bottom.

The mixture of vapor and liquid discharged by the tubes 24 and 26 into the annular chamber 55 strikes the bafile 51 substantially at right angles and thence turns downwardly. The vapor, in order to reach the connection to the superheater tubes 34 near the top of the vapor zone 44, must then turn abruptly upward and pass within the baffle 51. The impact of the mixture against the bafile 51 and the subsequent abrupt reversal of direction of the vapor cause the mixture to lose most of its liquid content and fall down to join the liquid in the drum 20.

It is significant that the drum 20, all the tubes 24, 26, 33 and 34, and the liquid 40, are entirely supported by the foundation 19, thus making it possible to use a relatively light casing structure 14, which is merely self-supporting. In Throckmorton et al. Patent No. 2,375,505, the heating surface assembly is hung from the top of the structural steel, and the casing must be made sufficiently strong to support the entire weight of those elements. It is very heavy compared with that of the invention.

The burners 28 are located in the floor of the radiant zone 21 and are directed axially into the space between the banks of tubes 24 and 26 so that the hot gases do not impinge directly against the tubes in this radiant zone. In this way the most efiicient use may be made of the combustion fuels wherein temperatures high enough to melt or damage the tube surfaces were the combustion products to impinge upon the tubes directly may be employed without causing such damage, while, however, the heat transmitted by radiation from such very hot gases will be absorbed without damage. It is to be noted that the drawing of Fig. 1 is not to scale as to the height of radiant section 21, this is merely as a matter of convenience. A usual design is to have the tubes in the radiant zone constructed of a length equal to about two and one half times the diameter of the tube bank circle. It will be noted that, in order to have such dimensions, the height of the vertical walls of radiant section 21 will be greater than at least one third of the combined height of the radiant section 21 and the convection section 23.

The modifications shown in Figs. 4 through 12 may be briefly described, because they can be arrived at by omitting elements of the furnace of Figs. 1, 2 and 3.

The unit illustrated in Figs. 4, 5 and 6 is substantially the same as that shown in Figs. 1, 2 and 3, with the exceptions that the forced draft fan 30, the economizer 32, the superheater 34 and the upper bafie 51 have been left out.

A drum 50 (Figs. 4, 5 and 6) entirely supported on a skirt 45 mounted on foundation 47 is filled with liquid 52 to a predetermined liquid level 54 by means of a liquid inlet 56 and a pipe 58. Vapor in the vapor zone 60 leaves the drum 50 through an outlet 62.

The furnace is provided with an integral stack 64 at the top.

Again there are two concentric banks of heating tubes 66 and 68, adjacent to the surface of the drum 50 and to the outer casing 70, respectively, the tubes being fired from burners '72 installed through the floor of the furnace.

As before, the burners 72 are directed upward, axially into the open space of the radiant zone between tubes 66 and 68 without impinging directly against the surface of these tubes. Here again, the drawing of Fig. 4 is not to scale, as the height of the radiant zone is actually much greater than that illustrated. Consequently there is ample space for the high temperature combustion products to give up heat by radiation and to be cooled down to the point where it is safe to have them impinge directly on the tubes in the convection zone.

A baflie 74 similar to that of Figs. 1, 2 and 3 is provided within the drum 50, and performs the same function. The baffle 74 is suitably supported as shown at 75.

The construction and arrangement of the casing 70, the drum 50, the tubes 66 and 68, the skirt 45 and the foundation is the same as in Figs. 1, 2 and 3.

Figs. 7, 8 and 9 illustrate a small furnace. The structure is very like that shown in Figs. 4, 5 and 6, except that the row of tubes 68 adjacent to the outer casing has. been omitted, and there is only a circular bank of tubes 102 adjacent to the surface of drum 10! also the unit is fired by tangential burners 104. Thus the drum 100 is shielded from receiving an appreciable amount of direct radiation by the tubes 102. It is to be noted that the burners 104 of the furnace are not directed axially but tangentially, so that the hot combustion products spiral upward and hence the vertical height of the radiant section of this furnace may be somewhat reduced relatively to the usual height as indicated in the other modifications illustrated. The hot combustion gases impinge against the furnace wall which is thus highly heated and reradiates heat to the tubes of the radiant section, although the gases do not impinge directly against any of said tubes.

It is to be noted that the furnace of Figs. 7, 8 and 9 is equipped with flue gas outlet 106, for connection to a separate stack, instead of having an integral stack, such as 17 of Fig. 1 or 64 of Fig. 4. This is a matter of choice.

It is to be noted further that while the showings of the various boilers is not to scale the shortening is done largely in the radiant zone since the usual ratio of convection section to radiant section is slightly greater than in the order of one to four, when considering the effective height of tubes in the radiant zone and the height of the finned tubes in the convection section.

Various other elements are shown in the several figures, for example, man holes 107, an access door 108, and an observation door 110 in Fig. 1; an observation door 112 in Fig. 4; a safety valve 114, access doors 116 and 118 and a blow-down connection 120 in Fig. 7.

It will be observed that in all the types of furnaces contemplated by this invention the radiant zone in each case is relatively tall, that is, at least as tall as the convection zone. This is for the reason that the radiant zone is designed to allow the burning of fuels at very high temperatures which temperatures would tend to melt or damage any boiler tubes or drum surface if the products of combustion impinged against such tubes or surfaces while at this temperature. In the arrangements of this invention heat is absorbed in this zone by radiation without damaging the absorbing surfaces by overheating, and in this way a very high percentage transfer of heat may be had from the burning of the fuel. For maximum efliciency the radiant zone must be tall enough to allow the temperature of the hot combustion gases to be cooled sufficiently so that they may then impinge against the absorbing surfaces with safety. It is usual to design vertical tube radiant heaters with tubes having a height in the radiant zone which is 2 /2 times the diameter of the tube bank circle.

The operation of the furnace of Figs. 1, 2 and 3 will be described as typical. Liquid charging stock enters the economizer 32, where it is preheated. From the economizer 32, the liquid 40 enters the drum 20, which is filled to the liquid level 42. The liquid at the bottom of the drum 2t) enters the tubes 24 and 26 and passes upward through them, being vaporized by direct radiation of combustion gases in the radiant zone 21 and by convection in the convection zone 23. The vapor passes from the tubes 24 and 26 into the vapor zone 44, and thence is passed through the superheater 34. Some liquid 40 in the annular or vapor-separating space between the baffle 48 and the drum 20 is vaporized by heat absorbed through same . 6. s the wall of the drum 20. This vapor passes upward to the vapor zone 44, where it joins the main body of vapor. The combustion gases pass upwardly through the radiant and convection zones 21 and 23, and thence leave through the stack.

The arrangement of outer andinner banks of tubes spaced apart in the radiant zone of the heater, as shown in Figs. 1 to 6 inclusive, has a definite advantage since both the outer wall of the furnace and this outer surface of the water drum are screened by the tube banks which very economically absorb heat in the radiant zone.

Obviously many modifications and variations of the invention as hereinbefore set forth may be made without departing from the spirit and scope thereof, and therefore only such limitations should be imposed as are indicated in the appended claims.

It is claimed:

1. A boiler construction comprising a combustion chamber having a relatively large and relatively tall radiant zone in the lower portion thereof and a smaller convection zone in the upper part thereof, a stack, a drum within said chamber and having its upper end above the lower portion of said convection zone and supported in large part by the foundation of said chamber, a restricted passage in said convection zone for maintaining proper flue gas velocity and formed by the wall of said chamber and the surface of said drum, an economizer supported in large part by said drum, means for filling said drum with fluid to a predetermined level, a bafile within said drum, the space within said baflie forming a downpipe which is not exposed to direct radiation and hence is free from vapor, inner and outer banks of vertical heating tubes within said chamber and surrounding said drum and supported in large part by said drum, a source of combustion gases between said banks, a forced draft fan for supplying air to said source, said inner bank shielding the surface of said drum against receiving an appreciable amount of direct radiation, a superheater supported in large part by said drum, and tubular means connecting the upper and lower ends of said tubes of said first and second banks to said drum above and below said level, respectively.

2. A boiler construction comprising a combustion chamber having a relatively large and relatively tall radiant zone in the lower portion thereof and a smaller convection zone in the upper portion thereof, a stack, a drum within said chamber having its upper end abovethe lower portion of said convection zone and supported in large part by the foundation of said chamber, a restricted passage in said convection zone for maintaining proper flue gas velocity and formed by the wall of said chamber and the surface of said drum, means for filling said drum with fluid to a predetermined level, a baflie within said drum, the space within said baflie forming a downpipe which is not exposed to direct radiation and hence is free from vapor, inner and outer banks of vertical heating tubes each bank having a single row of tubes surrounding said drum and supported in large part by said drum, a source of combustion gases between said banks, said inner bank shielding the surface of said drum against receiving an appreciable amount of direct radiation, and tubular means connecting the upper and lower ends of said tubes to said drum above and below said level, respectively.

3. A boiler construction comprising a combustion chamber having a relatively large and relatively tall radiant zone in the lower portion thereof and a smaller convection zone in the upper portion thereof, said radiant zone having vertical outer walls being at least one-third the height of both said radiant and convection zones together, asource of combustion gases, a flue outlet, a drum within said chamber and having its upper end above the lower portion of said convection zone and supported in large part by the foundation of said chamberpa restricted passage in said convection zone for maintaining proper flue gas velocity and formed between the wall of said' chamber and the surface of said drum, means for filling said drum with fluid to a predetermined level, a baffie within said drum, the space within said baffle forming a downpipe which is not exposed to direct radiation and hence is free from vapor, a bank of vertical heating tubes supported in large part by said drum and surrounding said drum and positioned adjacent to the wall of said chamber, and tubular means connecting the upper and lower ends of said tubes to said drum above and below said level, respectively.

4. A boiler construction comprising a combustion chamber having a relatively large and relatively tall radiant zone in the lower portion thereof and a smaller convection zone in the upper portion thereof, said radiant zone having vertical outer walls being at least one-third the height of both said radiant and convection zones together, a source of combustion gases, a flue outlet, a drum within said chamber and having its upper end above the lower portion of said convection zone and supported in large part by the foundation of said chamber, a restricted passage in said convection zone for maintaining proper flue gas velocity and formed between the wall of said chamber and the surface of said drum, means for filling said drum with fluid to a predetermined level, a baffie Within said drum, the space within said bafiie forming a downpipe which is not exposed to direct radiation and hence is free from vapor, a bank of vertical heating tubes supported in large part by said drum and within said chamber and adjacent to the outer surface of said drum, said bank shielding said surface from receiving an appreciable amount of direct radiation, and tubular means connecting the upper and lower ends of said tubes to said drum above and below said level, respectively.

5. A boiler construction comprising a vertical combustion chamber having a relatively large radiant zone in the lower portion thereof and a smaller convection zone in the upper portion thereof, a stack, a vertical cylindrical drum within said chamber and having its upper end above the lower portion of said convection zone and wholly supported by the foundation of said chamber, a restricted annular passage in said convection zone for maintaining proper flue gas velocity and formed by the wall of said chamber and the surface of said drum, an economizer wholly supported by said drum, means connecting said economizer to said drum for filling said drum with fluid to a predetermined level, a cylindrical baffle within said drum and concentric therewith and extending substantially from the bottom of said drum to said level, the space within said baffle forming a downpipe which is not exposed to direct radiation and hence is free from vapor, inner and outer circular banks of vertical heating tubes within said chamber and concentric with and surrounding said drum and wholly supported thereby, said inner and outer banks being positioned adjacent to the surface of said drum and adjacent to the wall of said chamber, respectively, burners installed in the floor of said chamber between said inner and outer banks, said inner bank shielding the surface of said drum from receiving an appreciable amount of direct radiation, a forced draft fan for supplying air to said burners, a superheater wholly supported by said drum and including a vertical heating tube outside said drum and adjacent thereto, means connecting said superheater to said drum above said level, and tubular means connecting the upper and lower ends of said inner and outer banks to said drum above and below said level, respectively.

6. A boiler construction comprising a vertical cylindrical combustion chamber having a relatively large radiant zone in the lower portion thereof and a smaller convection zone in the upper portion thereof, said radiant zone having vertical outer walls being at least one-third the height of both said radiant and convection zones together, a stack, a vertical cylindrical drum within said chamber and having its upper end above the lower portion of said convection zone and wholly supported by the foundation of said chamber, a restricted annular passage in said convection zone for maintaining proper flue gas velocity and formed between the wall of said chamber and the surface of said drum, means for filling said drum with fluid to a predetermined level, a cylindrical baflic within said drum and concentric therewith and extending substantially from the bottom of said drum to said level, the space within said baffle forming a downpipe which is not exposed to direct radiation and hence is free from vapor, inner and outer circular banks of vertical heating tubes within said chamber and concentric with and surrounding said drum and wholly supported by said drum, said inner bank being positioned adjacent to the surface of said drum, burners installed in the floor of said chamber between said banks, said inner bank shielding the surface of said drum from receiving an appreciable amount of direct radiation, and tubular means connecting the upper and lower ends of said tubes to said drum above and below said level, respectively.

7. A boiler construction, comprising a vertical cylindrical furnace chamber having a radiant heating zone and a convection heating zone, said chamber having a large radial width lower section of substantial height, a relatively small radial width upper section and a tapered or frusto-conical intermediate section, said lower section having vertical walls of greater height than the height of said intermediate section, a constant diameter water drum concentrically mounted within the furnace chamber, said drum extending vertically through all three of said sections, said convection zone comprising said upper section and being formed radially between said drum and the walls of said chamber to provide a narrow annular passage, said radiant zone comprising said intermediate and said lower sections together and being formed radially between said drum and the walls of said chamber to form a large open annular passage of substantial height to allow very high fuel temperatures in the open space, a pair of cylindrical banks of vertical boiler tubes within said chamber and concentric with and surrounding said drum, one of said banks of tubes lying adjacent to the outer walls of said chamber, the other of said banks of tubes lying adjacent to said drum and screening said drum from direct radiation in the radiant zone, a plurality of axially directed upshot burners peripherally spaced around the bottom of said radiant zone and located radially between said inner and outer banks of tubes so that the products of combustion do not impinge directly against said tubes in the radiant zone, said tubes being smooth in the radiant zone and having extended surfaces in the convection zone, and tubular means connecting the upper and lower ends of said tubes to said drum above and below the level of boiler liquid therein, respectively.

8. A boiler construction, comprising a vertical cylindrical furnace chamber having a radiant heating zone and a convection heating zone, said chamber having a large radial width lower section of substantial height, a relatively small radial width upper section and a tapered or frusto-conical intermediate section, said lower section having vertical walls of greater height than the height of said intermediate section, a constant diameter water drum concentrically mounted within the furnace chamber, said drum extending vertically through all three of said sections, said convection zone comprising said upper section and being formed radially between said drum and the walls of said chamber to provide a narrow annular passage, said radiant zone comprising said intermediate and said lower sections together and being formed radially between said drum and the walls of said chamber to form a large open annular passage of substantial height to allow very high fuel temperatures in the open space, a pair of cylindrical banks of vertical boiler tubes within said chamber and concentric with and surrounding said drum, one of said banks of tubes lying adjacent to the outer walls of said chamber, the other of said banks of tubes lying adjacent to said drum and screening said drum from direct radiation in the radiant zone, a plurality of axially directed upshot burners peripherally spaced around the bottom of said radiant zone and located radially between said inner and outer banks of tubes so that the products of combustion do not impinge directly against said tubes in the radiant zone, said tubes being smooth in the radiant zone and having extended surfaces in the convection zone, and tubular means connecting the upper and lower ends of said tubes to said drum above and below the level of boiler liquid therein, respectively, that portion of said tubular means connecting the lower ends of said outer bank including means for providing openings for said upshot burners to be directed therethrough.

9. A boiler construction, comprising a vertical cylindrical furnace chamber having a radiant heating zone and a convection heating zone, said chamber having a large radial width lower section of substantial height, a rela tively small radial width upper section and a tapered or frusto-conical intermediate section, said lower section having vertical walls of greater height than the height of said intermediate section, a constant diameter water drum concentrically mounted within the furnace chamber, said drum extending vertically through all three of said sections, said convection zone comprising said upper section and being formed radially between said drum and the walls of said chamber to provide a narrow annular passage, said radiant zone comprising said intermediate and said lower sections together and being formed radially between said drum and the walls of said chamber to form a large open annular passage of substantial height to allow very high fuel temperatures in the open space, a pair of cylindrical banks of vertical boiler tubes within said chamher and concentric with and surrounding said drum, one of said banks of tubes lying; adjacent to the outer walls of said chamber, the other of said banks of tubes lying adjacent to said drum and screening said drum from direct radiation in the radiant zone, a plurality of axially directed upshot burners peripherally spaced around the bottom of said radiant zone and located radially between said inner and outer banks of tubes so that the products of combustion do not impinge directly against said tubes in the radiant zone, said tubes being smooth in the radiant zone and having extended surfaces in the convection zone, tubular means connecting the upper and lower ends of said tubes to said drum above and below the level of boiler liquid therein, respectively, that portion of said tubular means connecting the lower ends of said outer bank of tubes being bent to provide openings for said upshot burners to be directed therethrough.

References Cited in the tile of this patent UNITED STATES PATENTS 482,384 Plunkett Sept. 13, 1892 545,386 Sparks Aug. 27, 1895 1,009,275 Barclay Nov. 12, 1911 1,126,685 Barclay Feb. 2, 1915 2,271,880 Wood Feb. 3, 1942 2,375,505 Throckmorton et al May 8, 1945 2,630,104 Harvey May 3, 1953 

